mmg_233_2014_genetics_genomicsfandomcom-20200215-history
Quorum Sensing
Quorum Sensing (QS) Quorum sensing is the regulation of gene expression in response to changes in the environment. QS is a way for bacteria to produce chemical signals, termed autoinducers, to communicate with each other; a main environmental change would be in the cell population or cell density in that environment. QS creates both interspecies and intraspecies cell-to-cell communications to form complex communities and complex structures. Function of Quorum Sensing QS exists to create communication between cells, mainly bacterial cells that coexist in a biofilm. The ability of bacteria to communicate with other bacterial cells has benefited the creation and growth of biofilms, host colonization, defense against competitors, and adaptation to changing environments. Understanding quorum sensing and cell communications can help subdue and eliminate bacterial infections. The Mechanism of Quorum Sensing Bacteria in nature mainly reside in the biological formation of a biofilm. A bacterial biofilm is a surface-associated microbial growth that has limited drug susceptibility, and can occur during bacterial infections. When in a biofilm, bacteria rely on upon interactions between different signal molecules to initiate gene expression. There are 3 different classes that quorum sensing is divided into: 1) Gram Negative Lux1/LuxR-type, 2) Gram Positive oligopeptide-two-component-type, and 3) Gram Negative and Gram Positive luxS-encoded autoinducer 2 (AI-2). Gram Negative Bacteria (GN) Acyl-homoserine lactones (AHL) are the signal molecules for quorum sensing in Gram Negative bacteria; AHL's freely diffuse across the cell membrane. AHL concentration is directly correlated to cell density in a biofilm. LuxR-like proteins are responsible for recognition of AHL's; once bound to AHL, LuxR-like protein binds to specific DNA promoter to target transcription genes. Each species of GN bacteria produces unique individual AHL molecules or a unique combination of AHL molecules. These unique molecules allow only that specific species to accept and respond to the signaling. Gram Positive Bacteria (GP) Type 1: This mechanism has three components: an autoinducing peptide (AIP), and a 2-component signal transduction system (TCSTS) which specifically responds to this AIP. These molecules don't readily diffuse through the membrane, so an ABC transporter is required to secrete AIP. Type 2: ComRS is a recently discovered type which occurrs in Gram Positive Streptococcus species, uses a sensing small-tryptophan signal peptide hormone called XIP. Once incorporated, XIP interacts with ComR, a regulator that encodes a master regulator, ComX. ComX later activates a later competent genes for genetic transformations. Resources Bassler, B. L. "How Bacteria Talks To Each Other." National Center for Biotechnology Information. U.S. National Library of Medicine, Dec. 1999. Web. 18 Oct. 2014. Jimenez, Juan Cristobal, and Michael J. Federle. "Quorum Sensing in Group A Streptococcus." National Center for Biotechnology Information. U.S. National Library of Medicine, 12 Sept. 2014. Web. 18 Oct. 2014. Li, Yung-Hua, and Xiaolin Tian. "Quorum Sensing and Bacterial Social Interactions ." National Center for Biotechnology Information. U.S. National Library of Medicine, 23 Feb. 2012. Web. 18 Oct. 2014. Desai, J. V., and A. P. Mitchell. "Fungal Biofilms, Drug Resistance, and Recurrent Infection." National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. 18 Oct. 2014.